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Measurement Units

 

In Hydro GeoAnalyst, measurement units can be specified in any field you like; however, the measurement units specified in the Parameter Editor (and during a Sample Import or when importing an AquaChem2014 project) are stored in a specific format and grouped into categories so that many of the views and modules will be able to perform unit conversions on demand.

Please Note: The dynamic measurement unit conversion is only available in HGA+.

 

In order for the unit conversions to work, parameter values stored in the underlying database use consistent units.  For example, all sodium results stored in the sample results table will be stored using one common measurement unit, typically milligrams per liter (mg/L), while PCE results may be stored in micrograms per liter (μg/L), and temperature is stored in degrees Celcius (°C).

Unit Categories

In many situations in Hydro GeoAnalyst, such as viewing the Sample List, creating plots in a Plot Collection, or generating a Sample Report, it may be preferable to work with or report values using units other than the measurement unit stored in the database.  In these cases, you may be provided with controls to select a different unit of measurement. In order to correctly convert units, Hydro GeoAnalyst relies on unit categories. Unit categories consist of units of measurement that share dimensionality - that is, they share the same dimension of base units: length (L), mass (M), time (T), and temperature (K). For example, the concentration (by volume) category is based on a dimensionality of M/L3 and includes the milligrams per liter, micrograms per liter, and milligrams per cubic meter. Furthermore, concentration units also include molar concentrations (e.g. moles per liter [mol/L] and milli-moles per liter [mmol]) for parameters with a specified formula molecular weight and equivalent concentrations (e.g. equivalents per liter [eq/L] and milli-equivalents per liter [meq/L]) for parameters with a specified formula molecular weight and valence.

 

Unit Conversion

Each unit category has one designated primary reference unit; all other units in the same category have conversion factors relative to this primary unit. For example, in Hydro GeoAnalyst the primary reference unit for the Time unit category is seconds and it has a unit conversion multiplier of 1 - all other units have conversion multipliers relative to seconds, as shown in the table below:

 

Unit

Name

Multiplier

Offset

Base

s

second

1

0

TRUE

min

minute

60

0

FALSE

hr

hour

3600

0

FALSE

day

day

86400

0

FALSE

yr

year

31557600

0

FALSE

 

Note the offset field is present to facilitate conversions for units with linear offsets such as the conversion from degrees Celcius to degrees Fahrenheit (i.e. °F = 5/9 x °C + 32).

 

Units and Importing Data

When importing data, you must also include specifications on the measurement unit of each parameter to be imported.  If the units are recognized by Hydro GeoAnalyst, the values to be imported will be automatically converted into the units associated with the parameter in the project (as specified in the Parameter Editor). If the units are not recognized, you will be asked to map the unrecognized unit to an existing one or add a new unit and conversion factors. Once a unit is added at the import step, it will be saved in the project for future use.

 

 


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